Content update - Preview events (user story 1878475) (#1332)

* Add article, toc, and redirects * Add a prerequisites section to 3 other event articles * Further edits * Update dotnet-desktop-guide/net/wpf/toc.yml Co-authored-by: Andy (Steve) De George <[email protected]> * Update article links * Minor clarification Co-authored-by: Andy (Steve) De George <[email protected]>
2026-09-08 23:43:29 +02:00 · 2022-03-14 15:26:19 -07:00
parent 084c3e0ba6
commit dd0052ecec
21 changed files with 616 additions and 2 deletions
@@ -0,0 +1,95 @@
+using System;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Controls;
+
+namespace CodeSampleCsharp
+{
+    //<EventSuppressionWorkarounds>
+    public partial class MainWindow : Window
+    {
+        public MainWindow()
+        {
+            InitializeComponent();
+
+            // Attach a handler on outerStackPanel that will be invoked by handled KeyDown events.
+            outerStackPanel.AddHandler(KeyDownEvent, new RoutedEventHandler(Handler_PrintEventInfo), 
+                handledEventsToo: true);
+        }
+
+        private void ComponentWrapper_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
+        {
+            Handler_PrintEventInfo(sender, e);
+
+            Debug.WriteLine("KeyDown event marked as handled on componentWrapper.\r\n" +
+                "CustomKey event raised on componentWrapper.");
+
+            // Mark the event as handled.
+            e.Handled = true;
+
+            // Raise the custom click event.
+            componentWrapper.RaiseCustomRoutedEvent();
+        }
+
+        private void Handler_PrintEventInfo(object sender, System.Windows.Input.KeyEventArgs e)
+        {
+            string senderName = ((FrameworkElement)sender).Name;
+            string sourceName = ((FrameworkElement)e.Source).Name;
+            string eventName = e.RoutedEvent.Name;
+            string handledEventsToo = e.Handled ? " Parameter handledEventsToo set to true." : "";
+
+            Debug.WriteLine($"Handler attached to {senderName} " +
+                $"triggered by {eventName} event raised on {sourceName}.{handledEventsToo}");
+        }
+
+        private void Handler_PrintEventInfo(object sender, RoutedEventArgs e)
+        {
+            string senderName = ((FrameworkElement)sender).Name;
+            string sourceName = ((FrameworkElement)e.Source).Name;
+            string eventName = e.RoutedEvent.Name;
+            string handledEventsToo = e.Handled ? " Parameter handledEventsToo set to true." : "";
+
+            Debug.WriteLine($"Handler attached to {senderName} " +
+                $"triggered by {eventName} event raised on {sourceName}.{handledEventsToo}");
+        }
+
+        // Debug output:
+        //
+        // Handler attached to outerStackPanel triggered by PreviewKeyDown event raised on componentTextBox.
+        // Handler attached to componentTextBox triggered by KeyDown event raised on componentTextBox.
+        // Handler attached to componentWrapper triggered by KeyDown event raised on componentTextBox.
+        // KeyDown event marked as handled on componentWrapper.
+        // CustomKey event raised on componentWrapper.
+        // Handler attached to componentWrapper triggered by CustomKey event raised on componentWrapper.
+        // Handler attached to outerStackPanel triggered by CustomKey event raised on componentWrapper.
+        // Handler attached to outerStackPanel triggered by KeyDown event raised on componentTextBox. Parameter handledEventsToo set to true.
+    }
+
+    public class ComponentWrapper : StackPanel
+    {
+        // Register a custom routed event using the Bubble routing strategy.
+        public static readonly RoutedEvent CustomKeyEvent = 
+            EventManager.RegisterRoutedEvent(
+                name: "CustomKey",
+                routingStrategy: RoutingStrategy.Bubble,
+                handlerType: typeof(RoutedEventHandler),
+                ownerType: typeof(ComponentWrapper));
+
+        // Provide CLR accessors for assigning an event handler.
+        public event RoutedEventHandler CustomKey
+        {
+            add { AddHandler(CustomKeyEvent, value); }
+            remove { RemoveHandler(CustomKeyEvent, value); }
+        }
+
+        public void RaiseCustomRoutedEvent()
+        {
+            // Create a RoutedEventArgs instance.
+            RoutedEventArgs routedEventArgs = new(routedEvent: CustomKeyEvent);
+
+            // Raise the event, which will bubble up through the element tree.
+            RaiseEvent(routedEventArgs);
+        }
+    }
+    //</EventSuppressionWorkarounds>
+}